1. Field of the Invention
The present invention relates to a solid-state imaging device and a driving method thereof, and more particularly to a solid-state imaging device suitable for such as smear reduction and the lowering of a readout voltage as well as a driving method thereof and an imaging apparatus.
2. Description of the Related Art
On a semiconductor substrate of a solid-state imaging device, a multiplicity of n-type region portions are formed in a p-well layer of a surface portion by being arranged in the form of a two-dimensional array to form a multiplicity of photodiodes (pn junction portions: photoelectric conversion elements). A metallic light shielding film provided with an opening above each photodiode is laminated on the surface of the solid-state imaging device. In the related-art solid-state imaging device, a predetermined potential is adapted to be applied to this light shielding film.
For example, in the related-art technique disclosed in JP-A-7-153932, a high-concentration impurity layer of an opposite conductivity type (p type) is formed on the surface of the above-described n-type region portion, and a contact hole is provided in an insulating layer laminated on the surface of the semiconductor substrate, so that the light shielding film and the high-concentration impurity layer are electrically connected through the contact hole. As a predetermined potential is applied to the light shielding film, the surface potential of the photodiode is set to the quasi-Fermi level or less of the high-concentration impurity layer.
Alternatively, as a potential lower than the surface potential of the photodiode is applied to the light shielding film, minority carriers (holes) generated by photoelectric conversion are allowed to escape to the light shielding film so as to reduce the recombination of signal charges (electrons) and the minority carriers.
With the related-art solid-state imaging devices, attempts have been made to reduce smear and the like by applying a predetermined potential to the light shielding film and by directly controlling the potential of the high-concentration impurity layer to a predetermined potential through the contact hole. However, in solid-state imaging devices in which millions of pixels or more are mounted as in the devices of recent years, the size of each single pixel (photodiode) is extremely small, so that it has become difficult to form a contact hole in each single pixel. In addition, the effect of metal contamination due to direct contact of the light shielding film with the semiconductor substrate through the contact hole has become such that it cannot be neglected. Accordingly, there has been a demand for improving the performance of the solid-state imaging device such as the reduction of smear through other methods.